In a statement issued after the call, Pentagon Press Secretary Navy Rear Adm. John Kirby said Hagel emphasized to his Russian counterpart how dangerous the situation in Ukraine remains and that Shoygu "reiterated his assurance that Russian forces would not invade."

Kirby said Hagel reiterated that the Ukrainian government has a right to preserve law and order within its own borders and also asked for Russia's help in freeing seven members of a military observer mission from the Ogranization for Security and Cooperation in Europe who are being held by pro-Russian militias in eastern Ukraine.

In addition, Kirby said Hagel called on Russia to observe an agreement negotiated earlier this month aimed at defusing the crisis and "repeated his call for an end to Russia's destabilizing influence inside Ukraine and warned that continued aggression would further isolate Russia and result in more diplomatic and economic pressure."

The warning came on the same day that the Obama administration imposed additional sanctions on Russian officials, businessmen and companies for Moscow's intervention in Ukraine.

Kirby said both leaders agreed to "have continued conversations seeking a way forward" on the Ukraine situation.